Coulomb forces in THz electromechanical meta-atoms

Thanks to their large sensitivity to electromagnetic fields, microelectromechanical systems are becoming attractive for applications in the THz band (0.1–10 THz). However, up to date all THz electromechanical systems couple electromagnetic fields to mechanical motion only through photothermal dissipative forces: such mechanism allows for sensitive detection but prevents applications that require coherent transfer of information. In this work, we present a THz electromechanical meta-atom where the coupling between an electromagnetic mode and the displacement of a metallic micro-beam is substantially controlled by a conservative Coulomb force due to charge oscillations in the nanometric-size capacitive part of the meta-atom. We present experiments, performed at room temperature, which allow distinguishing and precisely quantifying the contributions of conservative and dissipative forces in the operation of our electromechanical resonator. Our analysis shows that the Coulomb force becomes the dominant contribution of the total driving force for high-order mechanical modes. Such system paves the way for the realization of coherent THz to optical transducers and allows the realization of fundamental optomechanical systems in the THz frequency range.